During counterinsurgency operations, improvised explosive devices (IEDs) pose a great threat to conventional ground forces. IEDs have been based on a wide variety of explosive materials, including military explosives and propellants, agricultural materials (e.g. ammonium nitrate), industrial explosives, and a non-standard exotic chemical explosives (e.g. potassium chlorate or organic peroxides). Counterinsurgency strategy involves the determination of materials transfer points and IED manufacturing locations. Thus, there is a strong demand for explosives detection and identification. A simple, rapid and reliable method in the field would be a significant enabler of military operations.
Current technology deployed in the field for detection and identification of explosives has a number of limitations. Deployable lab systems using liquid chromatography and mass spectrometry for chemical identification are not acceptable for time-sensitive missions and require logistic support. In addition, hand held systems for chemical identification including IR spectroscopy (TruDefender) and Raman spectroscopy (FirstDefender) need bulk samples that are frequently not available. Other developing technologies include detection of volatile organic compounds (VOCs), often referred to as electronic nose or tongue technology. These comprise colorimetric and fluorescent arrays (see refs. 1-3), modified field effect transistors (see refs. 4,5), and modified quartz resonators (see ref. 6). The use of fluorescent semiconductor polymers for explosives detectors may detect common military-grade compounds used in homemade explosives and IEDs, including pentaerythritol tetranitrate (PETN). However, all these instruments require manual collection or analysis by persons directly at the suspect sites.
Remote sensing technology capable of detecting explosives at an appreciable distance, although highly desirable, has not been perfected despite considerable research. For example laser systems for standoff detection including hyperspectral imaging are of low sensitivity in soils, in that the target may be less than one pixel and signature may not be distinguishable from background.
A need exists for a simple and inexpensive method for detecting explosives, particularly using remote sensing.